Sandi, to answer your question, not as often as I should be!
In my prime, I did 30 minutes 5xs a week. But now I do it about 30 minutes a week - a sun salutation set every morning for about 5 minutes. I don't recommend videos. I HAVE yoga videos but I don't recommend them unless you've had a class. An instructor can see so much that you can't see. Until I felt comfortable with the poses and understood what alignment I needed to feel when I was doing those poses, a video did not do me any good.
My biggest advice is that yoga is internal. When you go to a class, they are all going to be skinny (unless you happen to live in Yogini's area). Don't worry about it. There will be poses that you do and you'll sweat like a pig and wonder, "How can I be sweating like a pig? I'm hardly doing anything." And you'll be embarrassed. Get over it. No one is watching you.
And Paula! You're right, 5 pounds is not much. But 14 pounds is a heck of a lot to gain.